A New In Vitro Bioassay System for the Discovery and Quantitative Evaluation of Mosquito Repellents

Mosquitoes vector many pathogens that cause human diseases. Repellents play a significant role in reducing the risk of these diseases by preventing mosquito bites. In this paper, we are reporting an Ali and Khan (A & K), large cage in vitro bioassay system that can effectively be used to measure repellency of compounds against mosquitoes. The system uses temperature as a landing and feeding stimulus, and collagen as a feeding substrate. The minimum effective dose (MED) of DEET (N, N-diethyl-meta-toluamide; 19.3 µg/cm2) against Aedes aegypti (L.) in a 30-cm2 treatment area from the A & K bioassay falls in the upper range of the in vivo, cloth patch bioassay (6-23 µg/cm2). Undecanoic acid and geranic acid, with MED values of 3.6 and 7.5 µg/cm2, respectively, in the A & K bioassay were active at 5.5-6.6 times lower dose than that in the in vivo bioassay. Thymol and methyl eugenol with MED values of 11.1 and 10.9 µg/cm2, respectively, were active at 3-4 times lower dose than that in the in vivo bioassay, whereas (-)-trans-p-Menthane-3,8 diol with MED value of 32.3 µg/cm2 was active at 1.3 times lower dose. Comparisons between 12-cm2 and 30-cm2 treatment areas, with similar concentration per unit area in the A & K bioassay, indicated that the MED values at 30 cm2 were 1-2 times higher. In addition to its use to identify the repellent properties of new products, the A & K bioassay can generate useful data on promising repellents to make in vivo testing and field evaluation decisions.